When long distance transmission is required in radar or in microwave telecommunications, it is necessary to have a hyperfrequency power source. Such sources are obtained either by using a low power source and then amplifying to the required power level, or else by using a high power oscillator which is synchronized to a low power oscillator. The most frequently used power stage components, when operating at more than 10 watts and in the X or Ku bands, are valve and avalanche diodes. Valve technology is old, and has certain advantages, but it is awkward to integrate with present day semiconductor technology. Avalanche diodes are single port devices and therefore they are not capable of being directly controlled and synchronized.